Spinning forming is typically utilized for ironing or drawing but is sometimes used as a method of increasing a thickness of a peripheral portion of a plate. For example, as shown in FIG. 9, PTL 1 discloses a method of sandwiching a plate 100 between a fixing base 110 and a pressing plate 120; and increasing the thickness of an overhanging portion 101 of the plate 100 while rotating the plate 100, the overhanging portion 101 overhanging from the fixing base 110 and the pressing plate 120.
According to the method disclosed in PTL 1, the fixing base 110 and the pressing plate 120 also serve as a die for a thickened shape. Specifically, the fixing base 110 and the pressing plate 120 are about the same in size as each other, and a tapered surface which decreases in diameter toward the plate 100 is formed at each of an upper portion of a side surface of the fixing base 110 and a lower portion of a side surface of the pressing plate 120.
According to the method disclosed in PTL 1, first, the entire overhanging portion 101 of the plate 100 is heated by a high-frequency heater. Then, a swaging die 130 including a forming groove having a substantially triangular cross section compresses the overhanging portion 101 until the swaging die 130 contacts the fixing base 110 and the pressing plate 120. With this, the overhanging portion 101 is formed to have an arrowhead-shaped cross section. According to the other drawings of PTL 1, the swaging die 130 is presumed to be a roller which rotates following the plate 100.